Specification Point 4.13:
Recall that chemical reactions are reversible, the use of the symbol ⇌ in equations and that the direction of some reversible reactions can be altered by changing the reaction conditions.
- Some reactions go all the way to completion and the reaction stops when all of the reactants are used up.
- In reversible reactions, the product molecules can themselves either react with each other or decompose and re-form the reactant molecules again.
- The reaction can occur in both directions: the forward reaction (which forms the products) and the reverse direction (which forms the reactants).
- When writing chemical equations for reversible reactions, two arrows are used to indicate the forward and reverse reactions.
- Each one is drawn with just half an arrowhead – the top one points to the right, and the bottom one points to the left:
A + 2B ⇌ AB2
- The direction of reversible reactions can be altered by adjusting some or all of the following reaction conditions:
- The direction of change depends on the chemical nature of the reactants and products and their physical states and properties.
Specification Point 4.14:
Explain what is meant by dynamic equilibrium.
- Reversible reactions can reach a state of dynamic equilibrium.
- Equilibrium occurs when the forward and reverse reaction proceed at exactly the same rate.
- Both reactions are taking place simultaneously but there is no overall effect on the concentrations of the reacting substances i.e. their concentrations remain constant at equilibrium.
- Equilibrium is dynamic i.e: the molecules on the left and right of the equation are constantly chemically changing into each other.
- It only occurs in a closed system so that none of the participating chemical species are able to leave the reaction vessel nor can any other substances enter.
Equilibrium can only be reached in a closed vessel which prevents reactants or products from escaping system
Edexcel GCSE Chemistry Notes
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Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.
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